DE2730625B2 - Process for the production of heavily tinned copper wires - Google Patents

Description

The invention relates to a method for the production of heavily tinned copper wires, in which a Gczcqener copper wire galvanically tinned and then Soft annealed or a copper wire first galvanically tinned, then through in its cross-section Drawing is reduced and then soft annealed.

For the production of electrical lines and circuits> tinned copper wire is often required, the tin layer has the task of simplifying the soldered connections. The Zimischicht can also serve as corrosion protection in some cases.

One method of making tinned wire is by making a copper wire passes through a vat of molten tin, taking the vat length and speed of the Copper wire are chosen so that in the course of the migration of the wire through the molten tin this is annealed at the same time and at the same time the work hardening resulting from the previous drawing processes is eliminated. The achievement of a centric edition according to this under the technical term »fire association« known method is associated with great difficulties. A strong eccentricity however, the overlay has a negative impact on the required soldering properties.

Another manufacturing option is to galvanize the copper wire and tin it then draw tinned copper wire to the desired final dimensions and in the same operation to anneal in a downstream continuous annealer. This procedure is used today on a large scale used in the manufacture of wires with thin layers of tin. As a result of economic reasons The high throughput speeds required are annealing temperatures above the melting temperature of tin required. As a result, layer thicknesses in the order of magnitude of J μιη cannot be exceeded without there being an eccentric tin plating.

The invention is therefore based on the object of applying the galvanic tinning process to this effect > Improve that with this process tinned copper wires with concentric layers of more can be produced as a 3—7 μπί layer thickness. This object is achieved in a method of the type mentioned in that a copper wire with

κι a low softening temperature lying below the melting temperature of the tin is used and the tinned copper wire drawn to finished dimensions for two to eight hours at one temperature below the melting temperature of the tin

ι> is soft annealed. The selected annealing temperature is at least 150 ° lower than in the previously known continuous galvanic interlocking systems usual temperature. It is also below the melting temperature of the applied tin, whereby

: i) a shift of the galvanic process in uniform layer thickness applied tin layer is avoided. The low annealing temperature that becomes possible through the use of a copper wire of high purity, but must last for a longer period of time

; · "To be maintained by the previous one Eliminate any solidification that has occurred in the copper wire when cold pulls. The low annealing temperatures but are sufficient to recrystallize the galvanically applied tin and thereby the

in whisker formation that is feared during tin-plating to avoid.

The long-term annealing of the tinned copper wires is expediently under non-reducing Atmosphere carried out in a pot oven.

ι, For annealing temperatures in the upper range of the soft annealing temperature range or for longer annealing times the diffusion layer that forms between copper and tin can be justifiable Go beyond measure. To avoid this difficulty

.. i speeds to a further aspect of the invention, a nickel layer of less than 2 μπι is proposed according to the front of the galvanic tinning galvanically applied to the copper wire. This nickel layer prevents or slows down as a diffusion barrier

i, re the diffusion layer formation between copper and Tin. The method according to the teaching of the invention can be used with particular advantage when A tin layer of 15 to 20 μm is applied to a wire with a diameter of 1.5 to 2.5 mm, which is tinned

ν wire pulled down to 0.5 to 0.8 mm and then the wire is annealed for at least 4 hours at a maximum of 155 ° C. The layer thickness of the The tin coating is then approx. 5 to 7 μm on the finished wire, but it can also be increased by applying larger amounts

■■■■:. Layer thicknesses or through smaller initial cross-sections be enlarged. For example, it is possible to use the method according to the invention to produce tinned Copper wires with tin layers of more than 10 μιτι To manufacture thickness.

t.i The invention is based on two exemplary embodiments explained in more detail.

Example I.

On a copper wire with a diameter of 2 mm

<, -> a tin layer of I8jim in an electroplating bath Wall thickness knocked down. In the same operation, the tinned wire is 0.7 mm in diameter pulled down. After pulling the wire it will open

Spezialtromnieln soft annealed in a long-term annealing at approx. 155 ° C and six hours duration in air. The annealed wire then has strength values between 200-250 N / mm ² tensile strength at line limit values of ^ 100 N / mm ² . The wires met all the conditions with regard to solderability even after severe aging. In this aging test, samples of the tinned wire are usually annealed at 155 ° C for 24 hours.

Example Il

On a copper wire with a diameter of 1.5 mm First a nickel layer in an electroplating bath

of 1 μηι and in the same or a separate one Operation a tin layer of 15 μπι deposited. The wire is then pulled down to a diameter of 0.5 mm and attached to special annealing drums Air is soft-annealed at 180 ° C for six hours. The existing nickel layer of approx. 0.3 μm is used the formation of a diffusion layer between copper and tin is prevented or slowed down. This ensures that diffusion layers of only a maximum 1.5 μπι can train.

The wires produced in this way fulfilled all the conditions with regard to solderability even after one aggravated aging.

Claims (4)

Patent claims: 1. Process for the production of heavily tinned copper wires in which a drawn copper wire galvanically tinned and then soft annealed or a copper wire first galvanically tinned, then reduced in its cross-section by drawing and then post-annealed, thereby characterized in that a copper wire with a low, below the melting point of Tin-lying softening temperature is used and the tinned one drawn to finished size Copper wire two to eight hours at a temperature below the melting point of the Tin is annealed. 2. The method according to claim 1, characterized in that that the soft annealing is carried out in the temperature range 170-140 ° C. 3. The method according to claim 1 or 2, characterized in that the softening in not reducing atmosphere is carried out. 4. The method according to claim 1 or one of the following, characterized in that before electroplating a nickel layer of less than 2 μιτι on the copper wire electroplated is applied.